The overall goal of this project is to understand how sensory signals are translated into commands for the control of movements. More specifically, the proposed experiments study the role of the primate superior colliculus (SC) and the pontomedullary reticular formation in the control of orienting movements of the eyes and head. The first set of experiments has two goals: 1) to describe the functional properties of neurons in the tecto-recipient regions of pontomedullary reticular formation during coordinated eye-head movements and during head movements in the absence of a gaze shift; and 2) to study the effects of microstimulation of these pontomedullary regions upon eye and head movements. These studies target the brainstem areas that receive dense projections from intermediate layers of SC and also have a high density of neurons projecting to regions of the spinal cord innervating the neck muscles. In the second set of experiments neurons in the rostral paramedian pontine reticular formation will be reversibly inactivated to see if the activity of these cells is critical for the eye and head components of coordinated eye-head movements or for head movements made in the absence of a gaze shift. The third set of experiments has three goals: a) to record from neurons in the superior colliculus using the same behavioral tasks that were used to record from cells in pontomedullary regions; b) to use a search strategy that will increase the probability of finding cells in deeper layers of superior colliculus with activity related to head movements; and c) to examine the possible contribution of collicular neurons to the unusual eye velocity profiles observed during large gaze shifts. The final set of experiments uses a novel method of varying the speed and amplitude of eye and head movements during a gaze shift while recording the activity of pontomedullary neurons in an attempt to understand how gaze, eye and head amplitude and velocity is encoded in the activity of pontomedullary neurons.